Adjustable transversely engaging brake



July 11, 1950 G. CURRIE ADJUSTABLE TRANSVERSELY ENGAGINGBRAKE 2 Sheets-Sheet 1 Filed Dec. 12, 1945 INVENTOR WITNESSES: I 20.1%.-

- G/len Curr/.

BL 4 G a-4416 ATTORNEY July 11, 1950 s. CURRIE AEJUSTABLE TRANSVERSELY ENGAGING BRAKE Fil ed Dec. 12, 1945 2 Sheets-Sheet 2 farce INVENTOR Gi/berf' Curr/ BY (Puffi WITNESSES:

ATTORNEY This invention relates thereof.

. made. i

' ing and burned out solenoidcoils mayresult.

Patented July 11, 1950 v N. P ,s-IATES PATENT: GOFFICE",

RANSVERSELY ENGAGING BRAKE ADJUSTABLE 'r 1 Gilbert Currie, Forest Hills, Pa assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania I Application December 12, 1-945, Serial No. 634,543

generally to brakes and is particularly directed to a brake which compensates brake wear,- misalignment of parts and requires no adjustment. throughout the life This invention in preferred form of embodiment is illustratedin connection with an elec- 'tric brake of the double-block type in which a spring applies'the braking torque and a solenoid operating against the spring or braking torques Forces applied in the proper direction to the free end of the bell crank drive the free extremities 'ofnthe. brake arms apart and release the brake.

Frequently on double block brakes the bell isactuated by a solenoid.

Most brakes of this general type have three adjustments, one for varying the torque and, hence, braking and releasingeffort by varying the amount of spring compression, one. for equalcrank 'izing the shoe clearances, usually :by'means of separate adjustments on the shoes and thethird for adjusting the stroke or travel of the solenoid plunger. i Y

While these adjustments .may vary for dif-' ferent types of brakes they are essentially the same. In the typical case, after the brake is mounted in position,- it is necessary to make I most and usually all of these adjustments, and,

the successful operation of the brake depends uponthe skill with which the adjustments are The initial adjustmentshowever, hold only for the initial thickness of the brake shoe lining. As-the brake is used and the linings are worn, the brake is continuously moving out ofadjustment. When the lining has worn an amount equal to the initial. shoe clearance, the solenoid plunger travel has been doubled and it is neces- 14 Claims. (Cl-18,8575) in substantiallyythe same direction whether.

Generally. it is an-object of this invention to providea brakeof the class described, in which .the probabilityof brake failure is-substantially reduced. Also itis anobject of this invention to PIOVide a brake which requires no adjustment when once put into, operation. 1 I Another object of thisinvention is to provide ,a; brake of theclassmentioned in which. automatic; compensation'for brake wear is had. Yet another objectofthisinvention'is to. pro

vide a .blakein which the travel of the operating ,mechanism for the brake remains constant irre- :spective of movement .of the brake shoes and arms-with weary x Still another object'of this invention is :to provideia brake; in which automatic compensation iorqmisalignment. of the brake wheel between the-brake .shoes is compensated.

And'still another object of this invention is Ito-provide a brake in which wear at the point of pivoting of the brake arms is compensated and does not efiect brake operation. Aiurther object of this invention is to.-providei a brake in which the forces acting on the brake arms at the points of pivoting thereof are the brake ison or off;

' Yet afurther objectof this: invention is to i provide a brake whichiseflicientin operation,

' {-A still further object of this invention is to --cons.istent in provide a brake which is simple in its elements, its operation and economicalto build.

. The foregoing objectsarelmerely illustrative .of the various aims and objects of this inyen- -tion.. Other objects and advantages. Willbecome -more*apparent upon a study of the-following specificationwhen consideredv in conjunction sary to readjust the. brake to restore the travel to its original amount. If the adjustments are not made at-the proper time, or not properly made, brake failures evidenced in excessive heatwith theaccompanying drawings, in which;

Figure 1 is a side view of an electromagnetically ,Fig. 2 is a'bottom View of the brake shown in Fig.1, v

Fig. -3 isaline diagram of; the brake of this invention illustrating the fforce's acting in the brake, and

Fig. 4 is a groupjof curves graphicallycomparing the operating characteristics of this invention with those of the conventional double blockrbrakeofthe electrically controlled type.

I to

i m d i the nuts which thread onto the extremities of members 4 and 9. Blocks 6 carry fixed projecting pins 8 which are the pivots-forthetwo memthe brake wheel have been separately described, it will be appreciated that these functions occur substantially simultaneously. Lever I9 terminates at its left end as viewed in Fig. 1 in an arcuate section 25 tapered in thickness having as its center the axis of pin 26. The arcuate section may ibegtoothed as agear segment, however, the provision of teeth isoptional, since, a smooth arcuate surface as shown, is known from actual reducbers of brake arm l0. Blocks 1 provide the end supports for shoulder pin 9 about which the two members of brake arm H jpivot. FBra'ke wheel l2 shown in position between the 'brake shoes l3 and I4 is usually supported in the position shown by means of the shaitiwhichiisitorbe controlled by the brake. Such a shaft is normally supported in bearings (not shown) forming'part of the mechanism to which it is connected. "-Brake'shoes l3 and M arerespectively connected to the-extremities o'f' bra'ke airms 1'0 and 'l l by means of pins Hand 16, the 'friction'forces at the points of pivoting of the brake shoes being "sufficiently 1 high to prevent the shoes from turnlng-thereabout under their own weight and preventing shoe drag on the"brake wheel when the brake is in releasedposition. An extension of the brake arm In to the riglit-of' -the fixed pivot 8 and' ben'eath the'brakewhe'el '12 terminates ad- 'jaicen't the fixed pivot 9 and 'at this extremity *carries'a: pin H. It-*is at' this point that-the iforces ffor actuating "the brake arm I I] are applied. "Brake arm 11 also has -anextenslon to theright of its fixed pivot 9 which carries-the pin 18 and at-which the 'actuatingforces are applied, It willibe noted that to apply the brakeshoes' to thebrake wheel -a-lforce acting 'dow-nwardlyas viewed in Fig. 1 must-be applied to pin 'l'l 'to reflect clockwiserotation'of brake arm "I'D. Gon

-'ver'se1y aforce acting "upwardly must -be applie'd *to thepin "18 to efiect counterclockwise rotation of the brake arm H. V

'?Movements of the brake arms are controlled by a 'pairo'f levers i9 and 20. Lever 'l9'i's a'ssembled of the three lever sections Ha, I 81) and I80 which "may be *welded" or otherwise suitably joined together to form a rigid-assembly. Lever 19 "is pivoted-about pin l'8=on the brake arm ll and "slida'bly pivoted about the pin I! 'on the 'bra'kearm lflby'means of the'slot2l. 'In order that the fixed pin 9 about whichthe brake =arm H'pi'vots may not inter-ferewith the movements of lever 9, a large circular opening 22 terminatlng in "the slot 2i and "surrounding fixed p'in 9. "i'sprovidedin the lever '19. Thus the lever-l9 "ls-supported at the points I-l and' lll-respectively 'onthe brake arms Hi and H aitwhich the opcrating :forces for the 'brake arms are applied.

Extension Hoof-lever 9 extendingfto theright, "of the points "of pivoting thereof "to the brake 'm'ms 1'0 and "H has? attached thereto the spring veyebolt 23. Theiorce eXerted-by'the spring-'assembly 24 "operating in compression' biases the .extension l9c of lever 19 upwardly, applying an 'fto -t'he, '-'p'ressure or shoe F4 on -the "wheel. While "the application "of the brake-shoes 1-3 and H to ti'on to practice to function equally well and provides an unlimited number of contacting points. Point 26 is selected as the center of the arcuate section 25 since it is substantially the center of rotationbf thelever 19 caused by angular movemerits of the brake arms (0 and H towards the brake Wheel as the brake shoe linings wear.

tremit'ies' in substantial-"sliding -=engagement rand tapering in thickness substantially 'to a point.

'LeVer-"ZU 'is also loosely :pivo'ted about :the fixed pin s about which brake arm H is pivoted. This isac'compli'shed "by providing :a, hole 28 in'the alever zll having a :diameter "slightly greater than the diameter o'fpin f 9. :Normally #gravity forces Willmaintainthe lever-mtintth position shownuin Whirzhthelostmottontin the counterclockwisezrotation-al direction :of lever 220- is taken :up. How- "ever, it m ay be desirable to'positively assure this condition in "which case a spring 29 disposed between the:springisupportingizmember 30? on brake arm at I -and the lever 120,;mayrbe1 utilized.

The arcuate .re'xtremities .of the levers 193and 20 as seen in .Fig. 2 are straddled by :the :pawl i3! '-Which forms the extremity :of .lever 132D :comprising:a part :of composite lever sassemblyd 2. iPawl 3 1 has-a V notch which engages with the correspondingly shaped xarcuate surface :of l-levers 19 and. "Thisllever 'assembly includes the two '1inks 32a:andf32b which are pivotallyjoined by the pin 33. A'spring 34 disposed between thelinks GZa-and 32b at :a point removed from the point of this pivotal joining "at .pin 33, angularly biases th iinks apart. Link 32aris pivoted about fixed pins-8.

This pivoting is accomplished by means of bushings 8a which :pivot on .the pins -8 and are 'each secure'din the sections of the brake arm I!) KseeFiguE). The side sections of the link 3200 are each pivoted about a reduced-section-of'the'bushings'fla. The lower extremity of the plunger '35 'ofthe-solenoid 38is pivotally'fastened to th link B'ZZJby the pin 31. The' 'expedientof utilizing the composite levers and pivoting these levers about bushings 8a is toprovide' means for biasing'the brake arm I'll tc-the left as viewed in Fig. -1 when the brake is 'in the off position. This will be treated more thoroughlyhereinafter in the-discussion of Fig. 3. As-illustrated in Fig. 1. the lever assembly -32"rests'uponthecross member 4 of the brakeframe and the fullweight of the solenoid plunger is borne thereby. Compression sprin 34 is compressed under this weight and the link 32?) moves angularly with respect to the link 3241. The "motion is'counterclockw-ise and by reason of the positioning of I the bearing J surfaces of pawl 3 I greater distance.

movement of the lever I9 pivoted to pins I1 and left of the vertical center line of the brake, the

angular relation of the levers l9 and changes, the pivoting thereof occurring about the axis of the pin 26 substantially at the center of rotation, but only in such a way as not to change the relationship of the pawl to the arcuate surfaces '25 and 2'1. That is, the spacing between the pawl and the arcuate surfaces does not measurably change. For example, if the brake wheel i to the right of the vertical center line of the brake, the pins I1 and I8 move through arcs about their fixed centers of rotation in a clockwise direction. Since pin "is located a greater distance from its center of rotation than pin I B, it moves the Consequently, the angular I8 is counterclockwise. Since pins 1'! and I 8 have both moved downwardly with respect to pin 9, the pin 26 in some slight measure has also followed dicate that the brake wheel is aligned with the vertical center line of the brake. It is to be understood, however, that misalignment within the limits for which the mechanism is designed does not adversely affect the operation, such misalignment being compensated by the levers I9 and 29.

As the brake lining wears the brake arm l0 pivots in a clockwise direction while the brake arm I! pivots counterclockwise. Thus pin l1 moves down and pin I8 moves up pivoting the lever I9 about its approximate center of rotation, that is, the axis of pin 26, in a counterclockwise direction. If the center of rotation of the lever I9 is exactly at pin 26 to whichlever 29 is pivoted, no translational movement of pin 26 with respect to fixed pin 9 will occur and consequently the lever 29 will not move. Should pin 26 be slightly to the right or to the left of this center of rotation of lever I9, then, of course, some slight translational motion of pin 26 with respect to pin 9 will occur and. the lever 20 will angularly move either counterclockwise or clockwise depending upon the direction from true center the pin 2-6 is located. This, however, is not detrimental.

When the solenoid is energized, the first portion of the movement of the plunger 35 causes the link 32b to pivot and engage the pawl 3| with the arcuate extremities of links I9 and 20, the link 32a being biased against the member 4 by the action of compression spring 34. Once the pawl 3| engages the mating surfaces and 21 of the levers, the links 3211 and 32b move together. Levers I9 and 20 are now actuated by the movements of the pawl and operate as a single lever, being held together by the component of the pawl pressure on the angled arcuate surfaces of levers I9 and 20, and by so designing the pawl lever 32b that the resistance of levers l9 and 20 to rotation act to increase the pressure of the pawl on these levers and thus prevent slipping of the paw on the arcuate surfaces 25 and 21.

During the first portion of clockwise rotational movement of the levers I9 and 20, pivoting thereof occurs about thepin I8 on brake arm II and lever I9 applies an upwardly directed force to the pin I! which rotates the brake arm [0 counterclockwise to remove the brake shoe l3 from the brake wheel. Meanwhile'the lost motion at the loose pivoting of lever 2|] to the fixed pin 9 is being taken up. When the lost motion at pin 9 is completely taken up the point of pivoting of the levers I9 and 29 shifts from pin I8 to fixed pin 9 and thereafter a downwardly acting force is applied to the pin l8 causing clockwise rotational movement of the brake arm II to remove brake shoe I4 from the brake wheel. When brake shoe I4 is lifted from the brake wheel the solenoid plunger reaches the end of its movement. The brake is now completely released and as long as the solenoid is maintained energized, the brake shoes are held clear of the brake wheel, without the use of an equalizing stop, the force maintaining this condition being that of the spring assembly 24 acting against the solenoid pull through different leverages on each of the levers I9 and 20.

The brake of this invention also compensates bearing wear at the points of pivoting of the brake arms I9 and II. The manner in which this is accomplished is illustrated in the diagrammatic showing of the brake in Fig. 3. Here the brake arms, levers, brake shoes and other com ponents are indicated in single line diagram for the purpose of simplicity, and parts corresponding to those of Figs. 1 and 2 have been given like reference characters.

Wear compensation at the points of pivoting 8 and 9 of the brake arms l0 and II results primarily from the fact that the forces acting on the brake arms at pins 8 and 9 are in substantially the same direction Whether the brake is on or off. That is, the direction Of radial thrust of the brake arms at their points of pivoting 8 and 9 does not reverse from the on to the ofi brake position.

This will be apparent from a study of the various forces represented by the arrows in Fig. 3 which act in the on and oif positions of the brake, the solid arrows representing forces acting in the on position of the brake, and the dotted arrows representing forces acting when the-brake is off. No attempt has been made to scale theforces, it being felt that a qualitative analysis is sufficient to illustrate the point being made. Forces in the brake lever system resulting from brake wheel drag on the brake shoes are not considered since they would only tend to complicate the analysis. It should be noted, however, that the following analysis holds in principle whether or not these forces are considered.

Arrows and 46, respectively, represent the forces acting on the brake shoes I3 and I4 as a result of the resistance to brake shoe movement offered by the brake wheel (not shown in Fig. 3). Arrows 41 and 48 represent the forces applied respectively to the pins I I and I9 at the'free extremities of the brake arms. These forces are applied by lever I9 being biased in the counterclockwise rotational direction by the spring force.

The forces represented by arrows 45 and 41 resolve in the component represented by arrow 49 acting in the approximate direction indicated .at

pin 8,:while forcesABa-nd 48 produce the component represented by arrow 56 acting in the approximate direction indicated at pin 9. Thus, in the brake on position the vectoral summation of forces on brake arm I result in a forcebiasing the :brakearm [hi] to the ,leftagainst pin 8 as viewed, while-the forces acting on the brake arm H effect a bias thereof to the right against pin 9. When the brake is to be released or moved to the off position and the solenoid is energized, pawl 31 is :thrust against the arcuate extremidoles of levers I9 and 20 .exerting a thrust thereon which acts to therigh-t as indicated by the dotted arrow 56. This thrust is applied to the pin !8 of the-brake arm H and thus acts as a force biasing :thefcbrake-arm H to the right represented by :dotted arrow 52. Lever 3.2, by reason of its pivoted connection to lever'32b carrying pawl 3i, is biased to the left :as indicated by dotted arrow 53, and this bias is applied to the brake arm 10 by means of the bushing 8. Since the levers l9 and ,2! are rotated in the clockwise direction by tion as the forces!!! and 5B. Thus, any lost motion in the pivoting of brake arms I0 and H at points 8 and 9 does not effect brake operation,

since the brake ar-m bias at their points of pivotingv is always in the same direction. Any wear which may occur at these bearing points resulting in a change in angular disposition of the brake arms is compensated by a change in angular relation of the levers I!) and 2E) much the same as compensationis afforded for'brake lining -wear as previously described.

It is thus apparent that need for adjusting the :travel of the solenoid plunger is eliminated since the plunger travel remains constant. All the variable factors resulting from brake wearand misalignment being compensated in changes in angular relation of the levers l9 and 20 and in changes of the points of engagement of the pawl 3| with the arcuate extremities of the levers.

Inorder to eliminate all adjustments, it is only necessary to provide a spring 1 or assembly of springs 24, as shown, with a small enough scale so that the difierence in shoe pressure between the condition of new brake lining and'that of old or worn brake lining,.does not vary more than 10%, in which case, the brake can be set for 110% of rated braking torque at the time of assembly andthe braking torque will not drop below 100% of the brakes rating when the linings have worn to the point where they should be replaced.

There are numerous other advantages inherent =in the brake of this invention besides the elimination of need for brake adjustments. One of these advantages is had in the provision of a switch '38, for example, a snap acting switch of conventional type, in such a position that the switch actuating member 39 will be engaged by the lever i9 when the brake lining has worn to a permissible limit. The switch 38 in any well known manner may control a light, a. bell or other warning device, thus indicating that the ;:brake liningsshould berenewed.

Another advantage resides in the fact that the angular relation of the levers serves as an {indication that the brake wheelie properly aligned with thebrake shoes thus eliminating the chances of misalignment.

Still another advantage results from the constant stroke of the solenoid plunger. As a consequence of this constant plunger stroke, thesolenoid does not have to develop an excessive pull, as; in the conventional type wherein the plunger stroke increases as the brake linings wear. Thus destructive hammer blows of the solenoid are measurably reduced.

A further reduction in hammer blows results from the change in leverage as the levers are actuated :by the solenoid and the solenoid does its work of compressing the brake spring 24. It will be remembered that the levers first pivot about pin I 8 and when the lost motion in the pivoting of lever 20 at pin 9 is taken up the pivot shifts to pin 9. In the first instance, when the solenoid air gap is maximum and consequently its pull least, the mechanical advantage at the solenoid is greater. As the air gap .decreases and the solenoid pull rises the leverage pivot shifts and decreases the mechanical advantage. This tends to more nearly matchthe available effort at the solenoid with the opposing mechanical forces.

The advantage of this is seen from the curves of Fig. 4 in which the solid curves 48 and 4| respectively designate the pull curve of the sole noid and the work to be done in the-brake of this invention and the dotted curves 42 and 43 respectively designate the pull curve of a solenoid and the work tobe done in a conventional ,double-block brakeas described in the preamble to this specification.

It will be seen that the pull curve for the conventional solenoid brake has considerablymore area than that required by the brake ofthis invention, and, since, when bothtypes of brakes are properly adjusted,the work to be done is the same, assuming equally rated brakes, the excess force in the conventional brake is absorbed in destructive hammer blows of the solenoid plunger.

With all brake designs the solenoid should pull in at a definite voltage or current. For example, the solenoids on alternating current brakes should pull in at about 85% of full voltage, the solenoids of direct current shunt brakes should pull in at of full voltage and the solenoids of direct current series brakes should pull in at 40% of full voltage. If the solenoid stroke varies, it is not possible to adjust the brake so that the above solenoid response is possible. With the brake of the present invention, this desirable operating characteristic is obtainable In alternating current brakes, the impedance of the solenoid coil varies inversely of the air gap between-the solenoid plunger and core. Thus a relatively low impedance of the coil exists when the magnetic circuit air gap is large. If the plunger fails to pullin, the coil currents are excessive and frequently result in burned out coils. The present invention by providing constant solenoid plunger travel and the change in leverage as the levers are actuated by the solenoid eliminates this trouble.

It is, of course, apparent that other arrangements of lever means may be utilized to effect the various desirable operating characteristics of the brake of this invention without departing from the spirit and scope hereof, which is namely that of the provisionpf ,a lever means so con- 9 'striicted and arranged inpivotal relation with the brake arms and with an actuating means that compensation for brake variables is obtained and a constant travel or stroke of the actuating means for operating the brake is provided.

*The foregoing disclosure and the showings made in the drawing are merely illustrative of the principles of this invention and are not to be interpreted in a limiting sense. The only limitations are tobe determined from the scope of the appended claims.

I claim as my invention:

1. A brake comprising, in combination, a movable member to be braked, a pair of brake shoes, a pair of brake arms mounted on pivots and one attached to each brake shoe for efiecting movement of said brake shoes to and from positions engaging said brake drum about the pivots of the respective brake arms, a first lever pivotally secured to both of said brake arms at points on each removed from the pivots of the respective brake arms, so that leverage for actuation of the brake arms is obtained, said first lever having a substantially fixed center of rotation defined by the arcuate movements of the points on said brake arms at which said first lever is pivoted, means for biasing said first lever in a direction to cause said brake arms to press said brake shoes against the brake drum, said first lever including an arcuate surface having as its center substantially the center of rotation of said first lever, a second lever mounted on a pivot on said first lever substantially at the center of rotation of the first lever and loosely pivoted to one of said brake arms substantially at the point of pivoting of said one brake arm, said second lever having an arcuate surface substantially of the same radius as the arcuate surface of said first lever, and means engageable with said arcuate surfaces for actuating said levers.

2. A brake comprising in combination, a member to be braked, a pair of brake shoes, a pair of brake arms mounted on pivots and one attached to each brake shoe for effecting movement of the brake shoes about the pivots of the respective brake arms, to and from positions engaging said member, a first lever pivotally secured to both of said brake arms at a point on each removed from the pivots of the respective brake arms so that leverage for actuation of the respective brake arms is obtained, means for biasing said first lever in a direction to cause said brake arms to press said brake shoes against said member, a second lever mounted on a pivot on said first lever between the points at which said first lever is pivoted to said brake arms said second lever also being pivoted substantially at the point of pivoting of one of said brake arms, and means for simultaneously actuating said levers.

- 3. A brake comprising in combination, a member to be braked, a pair of brake shoes, a pair of brake arms mounted on pivots and one attached to each brake shoe for effecting movement of the brake shoes about the pivots of the respective brake arms, to and from positions engaging said member, a first lever pivotally secured to both of said brake arms at a point on each removed from the pivots of the respective brake arms so that leverage for actuation of the respective brake arms is obtained, means for biasing said first lever in a direction to cause said brake arms to press said brake shoes against said member, a second lever mounted on a pivot on said first lever between the points at which said first lever is pivoted to said brake arms said secondlever auras also being loosely pivoted substantiaily at the point of pivoting of one of said brake arms, ta provide a predetermined limited lateral movement of said second lever at its-point of loose pivoting before angular movement thereof about the point of loose pivoting occurs, and means for simultaneously actuating said levers.

'4. A'brake comprising, in combination, a movable member to be braked, a pair of brake shoes,

a pair of pivotally mounted brake arms, one for each brake shoe, for actuating the brake shoes, a pair of levers, one of said levers being pivotally connected to both of said brake arms, the other of said levers being pivotally connected to said one lever at a point which is substantially the center of rotationof said one lever and also pivotally connected to one of said brake arms substantially at the point of pivoting thereof, means for biasing said one lever in one direction andmeans for-actuating both said levers in the opposite direction; 51 A brake comprising, in combination, a movablemember to be braked, a pair of brake shoes adaptedfor frictional engagement with said member, a pair of pivotally mounted brake arms, one for each brake shoe, for actuating the brake shoes to engage and disengage said member, a pair of levers, one of said levers being pivotally connected to both of said brake arms, the other of said levers being pivotally connected to said one lever betweenitheapoints of pivoting of said one lever to said brake arms and also loosely pivzoted tooneof said brake arms toprovide limited lateral movement thereof with respect to the point of pivoting, means for biasing said other lever in one direction laterally to take up the lost -motion at.the-.point of. loose pivoting thereof, means for biasing said one lever in a direction to actuate said. brake arms to apply said brake shoes to said member, and meansrfor biasing both of said levers in a direction to actuate said brake armsto remove-said brakeshoes from said member.

6. Abrake comprising .in combination, a member...to.-b,e braked-, .a-pair of brake shoes, a pair ofbrake arms mounted on pivots and one attached to each brakeshoe for effecting movement of the brakeshoes about the pivots of the respective brake arms, to and from positions engaging said member, a first lever pivotally 'securedato both of said brake arms at a point onreach removed from the pivots of the respective :brake arms so that leverage for actua" tion of the respective brake arms is obtained, means for biasing said first lever in a direction tocause said brake arms to press said brake shoes against said member, a second lever mounted on-a pivot on said first lever between the points at which said first lever is pivoted to said brake arms said second lever'also being pivoted substantially at the point'of one of said brake arms, each of said levers having-arcuate surfaces the centers' of which are substantially at the point of pivoting of the second lever to the first lever, a link pivotally mounted substantiallyvat the point of pivoting of said one brake arm, a second link pivotally attached to said first mentioned link andhaving a pawl thereon constructed and arranged to engage said arcuate surfaces of said levers, a resilient member biasing said links to a predetermined angular relationship, and means for actuating said second link. i y v 7. A brake comprising in combination, a member to be braked, a pair of brake shoes. a pair of brakearms mounted on;piv.ots. and one attached .to each brake shoe for effecting movement of; the brake shoes about the pivots of the respective brake arms, to and from positions engaging said member, afirst lever pivotally secured toboth of said; brake arms at a pointon each removed from the pivots of the respective brake arms, so that leverage for actuation ,of the respective brake arms is obtained, means for biasing said .first lever ina direction to cause said brake arms to press saidbrakeshoes against said member, a secondulever mounted on a pivot on said first lever between the points at which said first lever is pivoted ,to said brake arms said; second lever also beingpivoted substantially at the point of one of said brake arms, each ofsaid levers having arcuate surfaces the centers of which are substantially at the point of pivoting of the second lever to the first lever, a link pivotally mounted substantially at the point of. pivoting of said-one brake arm, a second link pivotally attached to said. first mentioned link and, having v a,:,paw1 thereon constructedand arranged to. engage said arcuate surfaces of said levers, and. means ,fQ actuating said second link.

. 8. An electromagnetic brake comprising. in combination, a member tobe braked,-at least two brake shoes adapted for engagement with said member, a pair of pivotally mounted brake arms, said brake shoes, being attached to-said' brake arms, a first lever pivotally mountedto both of said brake arms at points on the. brake arms removed from the points of pivoting thereof, means including a resilient member for biasing said first lever ina direction to move said brake armsto apply said brake shoes against. said. member, a second lever pivotally attached to .saidfirst. lever at a point between the points of pivoting of. said first lever on said brake arms and pivotallyattached to one of said brake .arms substantially at the point of pivoting thereof, an electric solenoid, and means attached to said solenoid for actuation thereby, constructed and arranged to engage both of said first and second levers 9. A brake comprising, in combination-, a memher to be braked, at least two brake shoes adapted for engagement with said. member, a pail-of pivotally mounted brake arms, said brake shoes being attached to said brake arms, a. pair of levers, means for securing said levers to said brake arms and to each other constructed and arranged to effect angular movement of. said levers in diiferent amounts in dependence of changes in angular. position of said .brake arms resulting from brakewear, means. for applying a bias to at least one of said levers to cause application of said brake shoes against said brake drum, and means for simultaneously moving-both of said levers in a direction opposite, to. that aiiected by said biasing means while :maintaining the angular relation of the levers,

10. An electromagnetic brake comprising, in combination, a rotatable-brakeydrum, a pairof brake shoes, a pair of pivotallymounted, brake arms, said brake shoes being attached 3 to said brake arms at points removed from the points; of

pivoting thereof, saidbrake arms beingdisposed on oppositesidesv of said brake .drumto effect movement of saidbrake shoev to andifromrposie tions engaging said-brake ,drum, on. opposite sides of said brake ;drum, ea ch:of; said jbrakearms having extension. arms terminating at; points; re.- moved from the points of pivoting thereof,,.th,e xtension-arm of one of said-brakearmsextendine sllbstantially to-the po nt-,of.pixot oe of the othen-ofgsaid brake arms, a first lever pivotally attached to both of said extension arms of said brakearms adjacent the extremities thereof, a second lever pivotally attached to said-first lever at a point betweenthe pivotalattachement thereoitosaid extension arms and also loosely pivoted aboutth point of-pivoting of said other brake armto-provide limited. lateral movement of the secondbrake arm-with respect to said point of pivoting of'said other brake arm, means including a resilient member for biasing said first lever and the brake arms in a direction to efiectapplication;- of said: brake shoes against said brake drum an :electric solenoid, a pawl and lever assembly-,constructedand arranged so that said pawl;simultaneos ly engages said first and, second levers tog-actuate ,saidfirst and second levers oppositely :to the actuation of the levers by said means including the, resilient member, and means .connectingsaid pawl lever assembly tosaid solenoidto be; actuated thereby.

11. A brake comprising, in combination,- a member ,to be braked, at least two brake shoes, a pairotpivotally mounted brake, arms, said brake shoes being attached; to said brake arms, said brakea-rms, upon movement thereof moving said brakeshoes to and from positions engaging said member, lever; means, a fixed pin, a pin on each of said brake arms at a point removed from the point, of pivoting thereof, said fixed pin being disposed between said pins on said brake arms, saidlever meansbeing pivotally mounted on. the pin on one of said brake arms, loosely pivoted about the fixed pin. to provide limited lateral movement thereof with respect to the fixed pin and; slidably pivoted. about the pin on the other of;.said:brake arms, and means for actuating said lever means.

12; A brake, comprising, incombination, a movable member to be braked,-. at least two brake shoes having surfaces thereon of aconfiguration to fit: said. member, first and second brake arms oneiattached toeach brake shoe, first. andsecond pivotameansa for. pivota-lly mounting said. brake arms. so. that angular movement of said brake arms ishad. to move said brake-shoes to and from positions engaging: said member, a first lever pivotally.attachedtoboth of said brake arms at aipoint. on each removed from each of said pivot means, a :secondlever-pivotally attached to said first lever at a point between the point of pivoting of. said first lever to .said first brake arm and said first pivot means, and. also loosely pivoted about saidIfir-st pivot means, means for angularly movingsai-d first and second levers in one direction, and means forangularly moving said first andsecondlevers .inthe opposite direction.

- 13;.A brake comprising, in combination, a member torbe braked, friction means for frictionally engaging said member to be braked, actuatinganeans formoving. said friction means to and from positions engaging said member to be braked; leverv means attached to said actuating means constructed and arranged to change its position in dependence of movements of said actuating-means. resulting from brake Wear and misalignment, means for biasing said lever means ina direction to effect movement of said actuating means. to. apply said friction means to said member-to ,bebraked, a.=movable.operating member; aportion ofsaid lever means being disposed in proximity,v ito said movable operating member and formed o that upon movement of said. lever means. as .az e nltzot;b echwear. nd. m sali nmen said erticn narmnver lative to said t ere ating member without changing the proximity relation thereto, said movable operating member being movable to and from positions to engage said portion of said lever means to effect movement thereof oppositely to said one direction to reverse the movement of said actuating means.

14. In a brake for a member to be braked, the combination of, friction means for engaging said member, movable actuating means connected with said friction means to effect operation thereof to and from positions engaging said member, lever means, pivot means mounting said lever means for angular movement, means providing engagement of said lever means with said actuating means at a point removed from said pivot means, said lever means having a surface thereof of a configuration so that the distance of all points thereof from a fixed point is substantially constant irrespective of angular movements of said lever means within its limits, a lever operator 14 pivotally mounted at a point adjacent said pivot means, a pawl pivotally mounted on said lever operator and having a part spaced a predetermined distance from said surface, said pawl being normally disengaged from said lever means and being operable through said distance to engage said surface of said lever means for effecting operation thereof.

GILBERT CURRIE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Cox Jan. 20, 1942 

